Ab Initio Effective Potentials for Use in Molecular Calculations

We have investigated the efficacy of ab initio effective potentials in replacing the core electrons of atoms for use in molecular calculations. The effective potentials are obtained from ab initio GI calculations on atoms and are unique and local. We find that the use of these effective potentials to replace the core orbitals of such molecules as LiH, Li2, BH, or LiH2, leads to wavefunctions in excellent agreement with all-electron ab initio results. The use of such effective potentials should allow ab initio quality wave-functions to be obtained for systems too large for the ab initio consideration of all the electrons.